It's the final third of the game left so I tried to estimate the amount of Skalds I have gotten but I'm somewhat at a loss. I lost count so long ago. But it's T906. The current number in the capital to create one is 36450 so I guess you can make a rough estimate from that if you count backwards how many there have been. For some comparison the second highest great person cost (to create the next one) in the capital is the Great Engineer at 5700 points ...
It's modern warfare now with planes and stuff so it's not unreasonable to get a Skald at least every 5th turn or so. About 5-9 units per turn tend to die during wars of the enemy. It's the peace-time in between that is now painful as it feels like the entire culture engine just stops as it can't compare to the free culture that the Skald brings into the world.
As noted I bought a few to but not to many, the cost to buy the next one is just 30k and I could do that at any time.
There are more great writers tho as bought Skalds doesn't increase the price at the capital for the once that you get "naturally". The price for the once you buy increase but it doesn't increase the cost of the natural once. So while you could count backwards how many I gained it will be the minimum amount since I also bought a few. A few was turned into cities, a few into great works and a few was used to push policies.
So is it to many? Perhaps. It hasn't done that much for the tech level but from a culture standpoint I'm crushing it. I am not about 4-5 policies ahead of the one in second place (China) and about 6-7 ahead of third and forth (Poly and it's either France, Denmark or Ethiopia).
But basically the first few once went to found cities on distant islands, then a fair amount went into great works and then in the end they are just treatises now that score 150k or around there per time used so probably to many Skalds.